1. Field of the Invention
The present invention relates to an image pickup device, and more particularly to an image pickup device for processing a digital signal.
2. Related Background Art
Many proposals have been made heretofore for a single plate color image pickup system, that is, a system in which an output signal from a single solid state image pickup device having a fine color filter arranged on an image pickup plane is processed. In a typical signal processing system thereof, a carrier component due to a color signal is eliminated by an output of a color image pickup device to produce a luminance signal, the carrier component is synchronously detected to separate the color signal, and the color signal and the luminance signal are separately gamma-processed and clipped to compose a video signal.
The size reduction and the weight reduction of the image pickup device which uses the single plate color image pickup system have been advanced as the recent electronics technologies develop. Among others, as the semiconductor technologies develop, a high speed analog-to-digital converter (AD converter) and a digital-to-analog converter (DA converter) are put into practice and a proposal has been made for a system which uses those technologies to digitize an output signal of the image pickup device such as a CCD and process the digital signal.
Namely, the color image pickup signal is analog-to-digital converted so that the filtering, the color separation and the signal processing such as the gamma processing, matrix processing and clipping are conduced in digital form, and they are digital-to-analog converted by a DA converter to produce a video signal.
However, in the image pickup device using the digital signal processing proposed in the prior art, a circuit used in an analog system is simply substituted by a digital system. As a result, a circuit scale is large, the number of components is large, a consumed current is large and the compaction of the device is not attained or the cost reduction is not attained
Further, in the prior art system, since a configuration thereof is not optimized for a digital system, a false outline is produced due to a quantization error which is inherent to the digital system or an over-range error, and the deterioration of a frequency characteristic and the reduction an image quality such as the reduction of a dynamic range occur.
Further, since a gain of a signal system is varied not by a digital signal but by an analog signal, a dynamic range is lowered, a non-linearity distortion is produced, a frequency characteristic is deteriorated, a circuit scale is increased and a consumed current is increased.